Net Earnings Per Share Net Earnings Per Share (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net Income (loss) Available to Common Stockholders, Basic	$ 63,529	$ 58,633	$ 157,513	$ 105,126
Weighted Average Number of Shares Outstanding, Basic	137,849	136,963	137,030	137,438
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1,570	1,000	2,000	1,000
Weighted Average Number of Shares Outstanding, Diluted	139,419	137,938	138,853	138,594